Phono-pickup



J. F. GORDON PHONO PICKUP Sept. 27, 1949.

Filed April 11, 1947 P WE P I 1 ii JAMES- F. GORDON Patented Sept. 27,1949 srArrs UNITE.

Q TEN PHQlgO-PICKUP h I James l f.--GordonTowsonfiMdg-assignw to Ben- Iv Application April This invention is directed to phonogr p k ups. Morespeciflca lly it is directed to magnetic phonograph pickups ofthe"type"employing"the modulated flux gap or variable reluctancep'rim cp .1 at. .L'v .ei, v

There are many ways Wherebythe intelligence activ br:generating elementin the pickup'is often a 'pi'eZoelectric'-"rystal 'whichf'generates asmall" electric purrent when 'itsfmechanical di mensionsare,alteredrorfoftenj small coil ofwire situ'atetil'inama'gnet'icr-fieldi "The-piezoelectric type-is 'usually referrjec'i tosimply as a' crystal pickupj'aiid"hasfoundwide application.-"Thef'piezdelectrivcrystal" used'insuchcrystal pickupsisunfortunatelyfsubject to "considerable variatiori of as uyham e"Zcharacteristics under varying conditions 'oftemperatureand' humidity;Thisfact, amongotherg has accelerated 'the dcvelo'piiientof othertypes'o'f pickups. The magneticHp'ckupj as described above:-'=is closelyana-lag'ous=to*-the conventional dynamoelectric generator of the typeemploying a permanent magnet to'supply its field' excitation, and aphonograph stylus tocsupply the relative motion between the armature, in:thiscasera 'coil -of wire, and the magnetic lines of forcen As can beunderstood from the foregoing analogy, the constructiori of such amagnetictpickup is usu'ally'. difiicult and expensive. ifbe'stvzres'ults 'are to'xbe obtained H It is an' bjectoflthis inventionto provide a phonograph pickupwwhi chiaziszrnot afie'ctedshy changes ofambient temperature.

It is a further object of this invention to provide 'aphonograph pickupwhich is not lfec' ted by-'therelative-humidity 'of'its environment;

It is a further object of this invention to provide a magneticphonograph pickup of simple construction.

It is a further object of this invention to provide a magneticphonograph pickup having good vertical compliance.

These objects are attained by the use of fixed pickup coils associatedwith a magnetic circuit the reluctance of which is varied by aphonograph stylus.

The above and further objects and novel features will more fully appearfrom the following detailed description when the same is read inconnection with the accompanying drawings. It is to be expresslyunderstood, however, that the drawings are for purposes of illustrationonly,

chief methods in" use at 'this nte'dstyluswhich cooperatesdix'Aviation-Corporation, TowsonrMds-acorn rpdratibnzof Delaware I 11,1947, Serial No. 740,840 (Cl. 179-100.)

t! and are not intended as a definition of the limits of the invention,reference for this purpose being had to the appended claims.

In the drawings, wherein like reference charref ke partsthroughoutthe"several inent df the instant end viewsiof 'the Fig i r aheehanicaroperation "-"Referrin'g o to F1 horseshoe m agnetf ffl haying strip 1|and lz se cur'e'd t'o the arms there The-"strips l hand 12 swam ed-t6'provide a arrow g-apfl 3 between them, and a stylus l4 astically-aifixedto'the strip's 'li I a-nd l 2 'by a' hioldd rubber piece =1 5.The stylu' M is bo rided t'd the pie'ce l5 which is -in tiirn on'dd tthe stiips- -Tl afid l2."- A pair of are 11 eany wound on the I IniFi'g.21 therelati' juxt A osition" of the ends of the strips ll and l2--attli g'ap il ii may be seen in greater detail. It will be noticed-thatthe strips ll and l' :aremot: coplanait butiithat one of the --casestrip 12 is" -slightly higher than theiedg'e of th'e strip I l--when thestylus I4 is in a verticalip'dsitiona This is the: rest position thatthe .lassemblyv maintains when no lateral force isapplieditoithestyluszl4.

f; Analyzing'lthe magneticcircuit now,where:

ear hen? ,t ea Lof the strips I I 8 or I dF=dls (3) Which tells us thatthe change in magnetic flux surrounded by the coils l6 and IT is alinear function .of the changes of dimension of the gap I3. It will beseen from Figs. 3 and 4 that 13 will be minimum when the stylus isdeflected to the left, as in Fig. 3, and will reach a maximum when p itis deflected to the right as in Fig. 4.

Considering now the voltage induced in the coils i6 and IT, by the lawof induction.

which states that the potential in the coils l6 and IT, or the potentialavailable at the terminals 18 is equal to the time rate of change ofdeflection of the stylus. This is the same as the equation for theaction of a conventional magnetic pickup.

Of course the strips. II and I2 must be quite flexible to allow easydeflection of the stylus 14 by the record groove, and the piece l5 mustbe sufliciently resilient to prevent the generation of spuriousmechanical modes. The piece l5 may serve the dual purpose of amechanical linkage and mechanical damping,

Although only one embodiment of the presen invention has beenillustrated and described in detail, it is to be understood that theinvention is not limited thereto. Various changes may be made in thedesign and arrangement of the parts without departing from the scope andspirit of the invention as the same will now be understood by thoseskilled in the art. For a definition of the limits of the inventionreference will be had primarily to the appended claims.

What is claimed is: 1. In a phonograph pickup: a permanent magnet; apair of resilient elements of magnetic material, one affixed to eachpole of the said magnet, said elements terminating in flat portionslying in close proximity and forming a gap in an otherwise completemagnetic circuit, corresponding major surfaces of said portions definingspaced mutually parallel planes when said portions are in a position ofrest, said elements being resilient only in directions normal to saidplanes; a stylus; and means cooperatively securingsaid'stylus to saidportions in a manner suchthat displacement of said stylus in aplaneperpendicular to said major surfaces varies the spacing of said planes,said means comprising a body of resilient material formed around saidstylus and bearing on the adjacent edges of said portions.

2. In a phonograph pickup: a permanent magnet; a pair of flat resilientelements of magnetic material, one affixed to each pole of said magnet,

said elements terminating in mutual proximity to form a gap in anotherwise complete magnetic circuit, corresponding major surfaces of theterminating portions of said elements defining spaced mutually parallelplanes when at rest; a stylus; and means resiliently securing saidstylus between said portions with its axis lying in a planesubstantially perpendicular to said planes, said means comprising a bodyof resilient material positioned between and bonded to said portions andhaving said stylus embedded therein, whereby movement of the point ofsaid stylus laterally with respect to said portions in one directionprogressively reduces the size of said gap while movement in theopposite direction progressively increases the size of .saidgap. V a

3. The combination as set forth in claim 2, said elements each having acoil formed around it, said coils being connected in series.

4. In a phonograph pickup: a permanent magnet; a pair of flat resilientelements of magnetic material, one affixed to each pole of said magnet,said elements terminating in mutual proximity to form a gap in anotherwise complete magnetic circuit, corresponding major surfaces of theterminating portions of said elements defining spaced mutually parallelplanes when at rest; a stylus; and a resilient member surrounding andbeing bonded to said stylus; said resilient member spanning the spacebetween said portions and supporting said stylus between said portionswith its axis lying in a plane substantially perpendicular to saidparallel planes, said resilient member transmitting force to saidportions in response to lateral movement to said stylus, wherebymovement of the point of said stylus laterally with respect to saidportions in one direction progressively reduces the size of said gapwhile movement in the opposite direction progressively increases thesize of said gap.

5. The combination as set forth in claim 4, said elements each having acoil formed around it, said coils being connected in series.

JAMES F. GORDON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'IENTS Number Name Date 1,778,048 Thomas Oct. 14, 19301,780,409 Thomas Nov. 4, 1930 1,792,554 Thomas Feb. 17, 1931 2,290,057Lindenberg July 14, 1942 FOREIGN PATENTS Number Country Date 334,551Great Britain Sept. 5, 1930

